Governments worldwide are currently working to expedite the rollout of covid-19 vaccination programmes for their citizens. Studies of the effectiveness of the Pfizer/BioNTech BNT162b2 vaccine and the AstraZeneca ChAdOx1 vaccine in Israel and the UK have shown that even a single dose of either offers substantial protection against the main variants of SARS-CoV-2 currently circulating in those countries.

However, these studies also reveal another, less welcome, phenomenon. In both studies, the odds of testing positive for SARS-CoV-2 appear to increase in the first week following vaccination, before protective effects have developed by about three weeks. It is not clear from either study why this effect occurs, but a recent survey of 2,070 older adults in England may provide a clue. Among those who had received the first dose of a vaccine less than three weeks previously, 41% reported meeting with someone indoors who was not a household member, care worker, or member of their “support bubble.” This was in violation of legal restrictions about indoor social contact that were then in operation. Given that during the period of data collection (15-20 February 2021), around 1 in 145 people in England were infected by SARS-CoV-2, these meetings will have been risky. 

Concerns that people may mistakenly assume that an initial dose of a covid-19 vaccine will provide immediate protection and will reduce their engagement in protective behaviours have been raised before. A previous survey within the UK conducted in early December 2020 suggested that 29% of people intended to follow pandemic-related rules and restrictions less strictly once they have been vaccinated, and another 11% “would probably no longer follow whatever coronavirus rules or restrictions were in place.” These intentions were particularly high among younger people. 

While not conclusive, the data from the Israeli and UK vaccine effectiveness studies are consistent with the hypothesis that some people are letting down their guard and contracting covid-19 in the days after being vaccinated, and before a degree of immunity has developed. In the UK, while the information given out to patients at their vaccination appointment does attempt to mitigate this problem, the relevant messages have not always been as clear nor as prominent as they might have been. In an eight page leaflet that was supposed to be provided to all patients at their appointment, it is not until page seven that patients are reminded that they still need to “practice social distancing, wear a face mask, wash your hands carefully and frequently, [and] follow the current guidance.” Patients who read that far may well feel this is at odds with the response to the question “Can I go back to normal activities after having my vaccine?” on page six, to which the answer is “Yes, you should be able to resume activities that are normal for you as long as you feel well.” More recently, NHS England have produced a new animation that attempts to tackle the issue more clearly, as well as talking points for their staff within vaccination centres to remind patients about the continued importance of taking precautions.  

As governments increase their efforts to maximise the uptake of vaccinations against SARS-CoV-2, identifying lessons from those countries that are further advanced with their campaigns is important. The emerging evidence from the UK suggests a particular risk may lie in the first few weeks following vaccination. We would urge governments to ensure that everyone who receives a vaccination is aware that it will not offer them adequate protection for at least the first three weeks, and that their ability to pass on infection to others is unknown. 

G James Rubin, King’s College London, Weston Education Centre, London.

Julii Brainard, Norwich Medical School, University of East Anglia, Norwich.

Paul Hunter, Norwich Medical School, University of East Anglia, Norwich.

Susan Michie, Centre for Behaviour Change, University College London.

Declaration of interests: Rubin and Michie participate in the UK’s Scientific Advisory Group for Emergencies and its subgroups. All authors receive funding from the UK’s National Institute for Health Research (NIHR). Brainard and Hunter receive funding from the World Health Organization. Hunter has an honorary position (unpaid) with Public Health England and receives funding from the European Union. 

Funding: Rubin, Brainard and Hunter are funded by the National Institute for Health Research Health Protection Research Unit in Emergency Preparedness and Response, a partnership between Public Health England, King’s College London and the University of East Anglia. Michie receives funding from the NIHR Policy Research Unit in Behavioural Science, a partnership between UCL, Newcastle, Warwick and LSHTM. The views expressed are those of the authors and not necessarily those of the NIHR, Public Health England or the Department of Health and Social Care. The funders played no role in the writing of this correspondence or the decision to submit for publication.