Where lockdowns are easing, is a second wave inevitable?

In the absence of a vaccination (most likely not before mid-2021¹) or medical treatments, containment measures have in some countries and regions been very effective at slowing the spread of SARS-CoV-2 within and between populations, ending the exponential growth in new case numbers observed in early 2020 (figure 1). Lockdowns are correspondingly being eased.

Figure 1: Confirmed COVID-19 cases by region, 7-day rolling average. Data source: Guidotti and Ardia (2020), COVID-19 Data Hub, https://covid19datahub.io. Compiled by PartnerRe Analytics.

However, as now evidenced by local outbreaks² in many of these countries, the SARS-CoV-2 virus is still very much with us. Contact tracing and quarantining are being used to contain these new outbreaks.

There is a common perception that such outbreaks are a ‘second wave’. This is not correct based on the low numbers involved. However, in my opinion the situation is now essentially a tinder box and second waves of COVID-19 before the end of 2020 are indeed a likely scenario. Why? Because:

Infection numbers now exceed 10 million globally – eradication, as with SARS-CoV-1, is therefore highly unlikely.

Every major pandemic since 1700 has had a substantial second peak in infection numbers approximately 6 months after the first.

SARS-CoV-2 is a ‘cluster champion’ – essentially the few infect the many (80/20 rule) via ‘cluster sites’ of any kind (e.g. public transport, major events, nightclubs, hospitals). These ‘super spreader’ incidents can quickly (especially if more than 4 to 5 days elapse without action³) lead to an explosion in case numbers. With lockdowns now easing in many countries, super-spreader incidents have become more likely. If caught early and tracing/quarantining is effective, the impact can be contained, but if not and the number of such incidents increases, the situation could quickly become unmanageable.

Transmission is likely to increase in the winter/colder seasons:

• People spend more time indoors in enclosed, often poorly ventilated spaces, increasing the chance of spread.
• Respiratory infections such as the common cold and influenza virus are more prevalent. As with SARS-CoV-2, these spread primarily via aerosols from sneezing and coughing. Such co-infections are therefore likely to increase the chance of spread of SARS-CoV-2.
• In the northern hemisphere, the winter/colder seasons arrive well before the expected earliest timing of a vaccine.

A vaccine is unlikely before mid-2021, and is not guaranteed.

Can we stop this happening? Must we return to full lockdowns until a vaccine and/or treatment is available? A recent UK study⁴ found that a combination (no one measure is sufficient) of social distancing, masks, case isolation and intensive contact tracing (traditional tracing, with improved results if combined with tracing apps), delivers the best results in containing SARS-CoV-2.

Therefore, as lockdowns are eased, these containment measures need to be maintained/applied and adhered to by the public in order to control the spread of SARS-CoV-2 (get and keep the R number below 1), and with particular attention to cluster sites.

Outbreaks will certainly continue to happen and are likely to increase for the reasons given above. However, whether these develop into a second wave will depend to a large extent on how consistently and on what timescale respective authorities apply the necessary containment measures, and on whether these are followed.