Government scientists have warned of concerns over any increase in foreign travel and the return of international students in September to the UK's battle against Covid.
Newly published documents show ministers were told that a surge in foreign trips could pose a risk due to the import of new variants.
A paper by the SPI-M modelling group from July 14 said: "Global surveillance, particularly on the emergence and control of novel variants of concern, and vaccination is required to bring infections worldwide under control.
"Any increase in foreign travel over the summer and the return of international students to universities in the autumn is of particular concern."
The warning came ahead of the Government's decision to press ahead with easing quarantine rules for double-jabbed arrivals from the EU and the US.
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Foreign Secretary Dominic Raab insisted the shift, which comes into force at 4am on Monday, were part of a "modest opening up".
But senior officials reportedly told the Government's Covid-O Committee on Wednesday that letting fully vaccinated Europeans in freely could risk lower quality vaccines undermining the battle against the virus.
The SPI-M document also warned that September and October would a "particularly risky point" in the pandemic, with risks to the NHS from return to schools and universities, and a greater resumption of normality.
It said: "It is likely behaviours will take time to return to more normal levels and, if this coincides with the return of schools and universities in the autumn, significant pressures on healthcare could be seen.
"This could be exacerbated by other normally seasonal infectious diseases increasing in prevalence."
It comes after England's deputy chief medical officer, Professor Jonathan Van-Tam expressed hope that the worst of the pandemic was over - but warned there could be "one or two bumpy periods" ahead.
Lockdown architect Professor Neil Ferguson also sounded an optimistic note earlier this week, when he said the "bulk of the pandemic" could be over by late September.
Another newly published paper warned that perspex screens in workplaces may actually increase the risk of spreading the virus.
The Scientific Advisory Group for Emergencies (SAGE) said there was very little evidence on whether the barriers work at reducing infection transmission through droplets.
And they warned that screens can increase the risk of virus transmission if they block airflow.
"There is some epidemiological and mechanistic evidence that suggests that screens could increase risks of aerosol transmission due to blocking/changing airflow patterns or creating zones of poor air circulation behind screens," the expert said.
Last month, No10 said the guidance around screens would not be changed despite a leaked Cabinet Office memo offering a similar warning.
