• The latest data from Public Health England (PHE) suggest that the COVID-19 vaccines currently deployed in the UK effectively reduce transmission within the community after a single dose.
  • Israel and Chile provide real-word evidence that different vaccines offer different level of protections against infection and that an effective vaccination campaign needs to be properly timed with the withdrawal of non-pharmaceutical interventions (NPIs) such as social distancing.
  • This is part of our rapid response content on COVID-19. You can view all briefings on COVID-19 vaccines produced by POST and the House of Commons Library in Vaccination and Covid-19.

With more than 60 million doses administered across the UK, including more than 22m second doses, data on the effectiveness of COVID-19 vaccines on virus transmission is increasing. This rapid response will describe the latest data on the effectiveness of COVID-19 vaccines on community transmission and the evidence considered at SAGE with regards to vaccination rollout, lifting of restrictions and impact on infection rate.

What is the latest evidence on COVID-19 vaccines and community transmission?

Clinical trials and real world data have proven that COVID-19 vaccines are effective in preventing symptomatic COVID-19 disease, hospitalisations and deaths (see previous POST’s rapid response on The performance of COVID-19 vaccines in clinical trials and in real world conditions). Since the beginning of immunisation programmes worldwide, data on the impact on transmission has been emerging (see previous POST’s rapid response on COVID-19 vaccines and virus transmission).

An initial study (not peer reviewed) from Public Health England (PHE) based on over 550,000 households in England monitored between January and March 2021 found that people who got infected 3 weeks after receiving one dose of the Pfizer/BioNTech or the University of Oxford/ AstraZeneca vaccine were between 38% and 49% less likely to transmit the virus to their household. According to the latest PHE COVID-19 vaccine surveillance report published on 20 May 2021, effectiveness for one dose of the Pfizer-BioNTech against infection is estimated to be between 55% and 70%, while for one dose of the Oxford-AstraZeneca vaccine it ranges from around 60 to 70%.

This is reflected at the community level. The latest data from the Real-time Assessment of Community Transmission (REACT) study showed that infection rates have halved since March and that around 1 in 1,000 people are now estimated to be infected in England. The study performed PCR tests on 127,000 volunteers between 15 April and 3 May and found that infection rates in people aged 55 to 64-years decreased from 0.17% to 0.06% between March and May, likely indicating an effect of the vaccination programme in this age group. The highest infection rate (0.21%) was among those aged 25 to 34 years.

COVID-19 vaccines and community transmission: international examples

Evidence from other immunisation programmes worldwide support the effectiveness of COVID-19 vaccines in reducing community transmission. However, they also show that different vaccines have different protection levels and that NPIs (non-pharmaceutical interventions) still have a key role to play in controlling disease spread. Israel and Chile can be used as examples to illustrate this (see Figure 1 and Figure 2).

Figure 1: Percentage of the population that is fully vaccinated in Israel and Chile. UK data are included as a comparison. Graph from'Our world in data'.

Figure 2: Daily new confirmed cases in Israel and Chile expressed as cases per million. UK data are included as a comparison. Graph from 'Our world in data'.

First case study: Israel

Israel started its vaccination programme on 19 December 2020. As of 20 May 2021, almost 60% of its population has received two vaccine doses (see Figure 1). Israel largely used the Pfizer / BioNTech vaccine, an RNA-based vaccine requiring 21 days between the first and the second dose. Israel’s latest exit strategy included three different phases:

  1. 7 February 2021: measures included reopening of open-air nature reserves and parks. 25% of the population was fully vaccinated at that point (40% received at least one dose);
  2. 21 February 2021: ‘green passes’ (a form of COVID-19 certification status) were implemented to access venues such as gyms and concerts. 35% of the population was fully vaccinated at that point (50 % received at least one dose);
  3. 7 March 2021: more restrictions were lifted, including on gatherings of up to 20 people indoors and 50 outdoors. 44% of the population was fully vaccinated at that point (57% received at least one dose).

Many considered Israel’s mass-vaccination campaign a success story that could be a model strategy for other countries. Its slow exit strategy (which still uses some NPIs, such as the use of masks in indoor public spaces) combined with the high effectiveness of the Pfizer/BioNTech vaccine in preventing infections after a single dose, ensured a significant and constant reduction of daily new cases (see Figure 2). There are currently around 3 new cases per day per 1,000,000.

Israel national surveillance data were published on The Lancet on 5 May 2021. The effectiveness of two doses of the Pfizer/ BioNTech vaccine against SARS-CoV-2 infection was estimated to be over 90% (95·3% for symptomatic infection and 91·5% for asymptomatic infection). A recent pre-print (not peer reviewed) analysing vaccination and infection data in Israel also suggests that high vaccine uptake in adults is highly correlated with indirect protection of unimmunised children under 16.

Second case study: Chile

Chile started its vaccination programme on 24 December 2020. As of 20 May 2021, almost 50% of its population has received two vaccine doses (see Figure 1). Chile employed two different vaccines. 93% of the population received the CoronaVac vaccine (an inactivated vaccine produced by the Chinese company Sinovac) and the remaining 7 % received the Pfizer/BioNTech vaccine.

Despite the fast vaccination rollout, Chile faced another wave of COVID-19 cases and on 1 April 2021 announced tighter restrictions, including border closures. There were 363 daily new cases per 1,000,000 (see Figure 2). Only 20% of the population was fully vaccinated at that point (see Figure 1) and over 35% received at least one dose.

This spike in cases in Chile appears to have been a result of:

What has been discussed by the Scientific Advisory Group for Emergencies (SAGE) about the vaccination rollout and the lifting of restrictions?

The success of the COVID-19 vaccination campaign is the first criterion considered in the Government’s COVID-19 Response – Spring 2021 (the Roadmap) to allow the gradual lifting of restrictions. The Scientific Advisory Group for Emergencies (SAGE) has discussed in several meetings the relationship between vaccination rollout, the lifting of NPIs and an increase in transmission:

Acknowledgements

POST would like to thank Professor Adam Finn (University of Bristol; Bristol Royal Hospital for Children) who acted as external peer reviewer in preparation of this article.


Photo by Just Jack on Unsplash

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