Table 2 Highlights of the link between COVID-19 and Alzheimer’s disease

Impact of COVID-19 on AD

Effect on dementia severity

1. COVID-19 and prolonged hypoxia would exacerbate severity of pre-existing cognitive impairment of AD

2. COVID-19 pandemic and related restriction aggravate cognitive impairment in AD

Effect on neuropsychiatric symptoms

1. Clinical presentations of COVID-19 in AD patients are atypical, and neuropsychiatric symptoms are common

2. COVID-19 leads to the worsening of pre-existing neuropsychiatric symptoms in AD

3. COVID-19 pandemic and related restriction aggravate neuropsychiatric symptoms in AD

4. Worsened hyperactivity and bizarre behaviors emerge in AD animal model after isolation

Effect on disease progression

1. There is no consensus on the effect of COVID-19 pandemic and related restrictions on dementia progression in AD patients

Trigger for AD

1. AD-like features are involved in COVID-19 neuropathology

2. SARS-CoV-2 intrudes brain structure and causes brain functional abnormalities at 6-month longitudinal follow-up

3. Increased risks of memory problems and AD are shown at 12 months following acute COVID-19 infection

4. COVID-19-related social isolation and loneliness increase the risk of cognition decline and future dementia

Impact of AD on COVID-19

Vulnerability to COVID-19 infection

1. AD patients are at increased risk of COVID-19 infection

2. Biological and socioeconomic factors work together to make individuals with AD vulnerable to COVID-19 infection

Prognosis of COVID-19 infection

1. Pre-existing dementia is associated with the largest risk of COVID-19 hospitalization and mortality

2. Age, comorbidities, APOE ε4 allele, and OAS1 gene variant are associated with poor outcomes of COVID-19 infection

Management of AD during COVID-19 pandemic

Modification of care strategies in AD

1. The COVID-19 pandemic profoundly changes the way of AD management

2. Telemedicine is feasible and well accepted in assessing and managing AD during the COVID-19 pandemic

Potential impact of drug therapies for AD on COVID-19

1. Cholinesterase inhibitors therapies have not been reported on reducing the infection rate and mortality of COVID-19 thus far

2. Prescribing ARBs but not ACEIs is significantly associated with a lower risk of COVID-19 occurrence among AD patients

3. The impact of CCB usage upon the efficacy of COVID-19 in AD patients remains to be clarified

Effect of COVID-19 vaccines on AD

1. Vaccinated AD patients are still at increased risk for COVID-19 breakthrough infection

2. AD patients may be vulnerable to delirium after taking the COVID-19 vaccine

3. Accelerated focal amyloid-β deposition induced by low-level inflammation after COVID-19 vaccination in AD patients

4. The combination of anti-amyloid-β immunotherapies and adenoviral COVID-19 vaccines may increase the risk of cerebral hemorrhage in patients with AD

Mechanisms of the link between COVID-19 and AD

1. Inflammation, aging, insulin resistance, acetylcholine, and amyloid-β might mediate the mechanistic links between COVID-19 and AD

2. Risk alleles of APOE and OAS1 are associated with both AD and poor COVID-19 outcomes

3. Dysregulated immunity may play a key role in the mechanistic link between COVID-19 and AD